Micronutrients, Water and Dietary Fibre

Defining Micronutrients

The spec gives a precise definition here too: micronutrients are “required by humans throughout life in small quantities to facilitate a range of physiological functions.” Unlike macronutrients (protein, fats, carbohydrates), which are consumed in gram amounts, micronutrients are needed in milligram or even microgram quantities. The two categories are vitamins and minerals (plus trace elements). Despite their small quantities, deficiency — or excess — of any micronutrient has measurable health consequences.

Fat-Soluble Vitamins: A and D

Vitamin A exists in two forms: retinol (from animal sources such as liver, oily fish, eggs and dairy) and beta-carotene (a provitamin found in orange and dark-green vegetables such as carrots, sweet potato, spinach — converted to vitamin A in the body). Its functions include: maintaining normal vision in dim light (deficiency causes night blindness); supporting the immune system; and maintaining healthy skin and mucous membranes. Excess vitamin A from supplements is toxic and teratogenic in pregnancy — pregnant women are advised not to eat liver for this reason. Fat is needed in the diet for vitamin A to be absorbed, because it is fat-soluble.

Vitamin D is uniquely made in the skin through exposure to UVB sunlight — during UK winters (October to March), sunlight is too weak to trigger synthesis, so dietary sources become critical. Food sources include oily fish (salmon, sardines), egg yolk, and fortified foods (some cereals, margarine, plant milks). Its primary function is to promote calcium absorption in the gut, enabling bone mineralisation and muscle function. Deficiency causes rickets in children (soft, bowed bones) and osteomalacia (soft, painful bones) in adults. The NHS recommends a 10 μg vitamin D supplement for everyone in the UK during autumn and winter.

Water-Soluble Vitamins: B Group and Vitamin C

The B vitamins work primarily as coenzymes — they help enzymes release energy from macronutrients. Most B vitamins are not stored in the body in large amounts and must be consumed regularly. Key B vitamins on the spec:

B1 (thiamin) — supports the release of energy from carbohydrates; found in wholegrain cereals, pork, peas. Deficiency: beriberi (nerve and heart damage), seen historically in populations reliant on polished white rice. B2 (riboflavin) — assists energy release from all macronutrients; found in dairy, meat, eggs and green vegetables. Deficiency: sore throat, cracked lips, and inflamed tongue. B3 (niacin) — needed for energy release and DNA repair; found in meat, fish, wheat flour, eggs. Severe deficiency: pellagra (dermatitis, diarrhoea, dementia). B9 (folic acid / folate) — essential for DNA synthesis and cell division; found in leafy green vegetables, fortified cereals, pulses, liver. Critical in the first twelve weeks of pregnancy: deficiency causes neural tube defects (spina bifida) in the developing foetus. Women planning a pregnancy are advised to take a 400 μg supplement daily. B12 (cobalamin) — required for red blood cell formation and nerve function; found exclusively in animal products (meat, fish, eggs, dairy). Vegans are at high risk of B12 deficiency and must supplement or eat fortified foods (fortified plant milks, nutritional yeast). Deficiency can cause megaloblastic anaemia and neurological damage.

Vitamin C (ascorbic acid) is vital for: collagen synthesis (the protein that forms connective tissue, skin and blood vessel walls); immune function; and the absorption of non-haem iron from plant foods (vitamin C reduces ferric iron to the more absorbable ferrous form). A glass of orange juice with a bowl of iron-fortified cereal significantly improves iron uptake — an example of complementary nutrient action. Deficiency causes scurvy (bleeding gums, poor wound healing, bruising). Vitamin C is heat-labile and water-soluble, making it the most vulnerable vitamin during cooking — another reason to prefer steaming over boiling.

Minerals: Calcium, Iron, Potassium and Magnesium

Calcium is the most abundant mineral in the body — 99% is in bones and teeth. It requires vitamin D for absorption. Adolescents have particularly high calcium needs during the rapid bone growth of puberty. Deficiency over a lifetime leads to osteoporosis (reduced bone density) and increased fracture risk. Sources: dairy, fortified plant milks, leafy greens, tinned fish with bones (sardines, salmon). Iron comes in two forms: haem iron (in red meat and offal — highly absorbable) and non-haem iron (in fortified cereals, dark-green vegetables, pulses — less absorbable, but absorption is improved by vitamin C). Deficiency causes iron-deficiency anaemia: reduced haemoglobin production means less oxygen is carried in the blood, resulting in fatigue, pallor and breathlessness. Teenage girls and women of childbearing age are at highest risk due to iron losses during menstruation.

Potassium maintains fluid balance, supports nerve impulse transmission and helps regulate blood pressure. Found in bananas, potatoes, spinach, pulses and dairy. Adequate potassium intake is associated with reduced risk of hypertension (high blood pressure). Magnesium is needed for enzyme activity, muscle contraction and bone health. Found in nuts, seeds, wholegrains, dark-green vegetables. Deficiency symptoms include muscle cramps, fatigue and irregular heartbeat.

Trace Elements: Iodine and Fluoride

Iodine is required to synthesise thyroid hormones (thyroxine), which regulate metabolic rate, body temperature, and growth. Sources: seafood, dairy, eggs. Deficiency causes goitre (enlarged thyroid gland) and, in children, cretinism (impaired brain development and stunted growth). Many people in the UK obtain iodine through dairy, but vegans who avoid dairy and seafood are at risk — some plant milks are now fortified with iodine. Fluoride strengthens tooth enamel by incorporating into the crystalline structure of the mineral hydroxyapatite, making teeth more resistant to acid attack from bacteria. It is found naturally in some water supplies (water fluoridation is practised in some UK regions), in tea, and in fluoride toothpaste. Deficiency: increased susceptibility to dental caries (tooth decay). Excess fluoride causes dental fluorosis (white or brown mottling of teeth).

Dietary Value of Water

Water is not a nutrient in the macronutrient / micronutrient sense, but it is essential for life. The body is approximately 60% water by weight. Water’s functions include: transporting nutrients and oxygen in the blood; removing waste products (urea via the kidneys); regulating body temperature through sweating and breathing; providing a medium for all chemical reactions in cells; and lubricating joints. Adults in the UK are advised to drink approximately 6–8 glasses (1.5–2 litres) of fluid per day — more in hot weather or during exercise. Dehydration reduces concentration, causes headaches, and — if severe — impairs kidney function. For a teenager playing football for 90 minutes in summer, fluid replacement during and after the match is critical to maintain performance and avoid heat exhaustion.

Dietary Fibre (NSP)

Dietary fibre (non-starch polysaccharides, NSP) is the indigestible part of plant cell walls — found in wholegrain cereals, fruit, vegetables, pulses, nuts and seeds. Because it cannot be digested in the small intestine, it passes to the colon, where it: bulks out faeces and speeds intestinal transit (reducing the risk of constipation and bowel cancer); feeds beneficial bacteria (promoting a healthy gut microbiome); and slows glucose absorption after a meal (helping to maintain stable blood sugar levels). Adequate fibre intake also promotes satiety — the feeling of fullness — which can help manage weight. The UK recommendation is 30 g of fibre per day for adults; most people consume closer to 18 g. Switching from white bread to wholemeal, or adding a portion of pulses to a stew, makes a significant difference.